MySQL :: MySQL 8.4 参考手册 :: 15.8.3 帮助语句

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MySQL 8.4 参考手册 / 15 条 SQL 语句 / 15.8 实用程序语句 / 15.8.3 帮助语句

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15.8.3 HELP 语句15.8.3 HELP Statement

HELP 'search_string'

HELP 语句从 MySQL 参考手册返回在线信息。其正常操作需要在 mysql 数据库中使用帮助主题信息初始化帮助表（参见第 7.1.17 节，“服务器端帮助支持”）。The HELP statement returns online information from the MySQL Reference Manual. Its proper operation requires that the help tables in the mysql database be initialized with help topic information (see Section 7.1.17, “Server-Side Help Support”).

HELP 语句在帮助表中搜索给定的搜索字符串并显示搜索结果。搜索字符串不区分大小写。The HELP statement searches the help tables for the given search string and displays the result of the search. The search string is not case-sensitive.

搜索字符串可以包含通配符字符 % 和 _。这些字符在 LIKE 操作符的模式匹配操作中具有相同的含义。例如，HELP 'rep%' 返回以 rep 开头的主题列表。The search string can contain the wildcard characters % and _. These have the same meaning as for pattern-matching operations performed with the LIKE operator. For example, HELP 'rep%' returns a list of topics that begin with rep.

HELP 语句不需要诸如 ; 或 \G 之类的结束符。The HELP statement does not require a terminator such as ; or \G.

HELP 语句理解几种类型的搜索字符串：The HELP statement understands several types of search strings:

在最一般的层面上，使用 contents 来检索顶级帮助类别的列表：At the most general level, use contents to retrieve a list of the top-level help categories:
```
HELP 'contents'
```
要列出给定帮助类别中的主题，例如 Data Types，请使用类别名称：For a list of topics in a given help category, such as Data Types, use the category name:
```
HELP 'data types'
```
要获取特定帮助主题的帮助，例如 ASCII() 函数或 CREATE TABLE 语句，请使用相关的关键字：For help on a specific help topic, such as the ASCII() function or the CREATE TABLE statement, use the associated keyword or keywords:
```
HELP 'ascii'
HELP 'create table'
```

换句话说，搜索字符串可以匹配一个类别、多个主题或单个主题。下面的描述说明了结果集可能的形式。In other words, the search string matches a category, many topics, or a single topic. The following descriptions indicate the forms that the result set can take.

空结果Empty result
未找到与搜索字符串匹配的内容。No match could be found for the search string.
示例：HELP 'fake'Example: HELP 'fake'
产生：Yields:
```
Nothing found
Please try to run 'help contents' for a list of all accessible topics
```
结果集包含单行Result set containing a single row
这意味着搜索字符串找到了一条匹配的帮助主题。结果包括以下内容：This means that the search string yielded a hit for the help topic. The result includes the following items:
- name：主题名称。name: The topic name.
- description：该主题的描述性帮助文本。description: Descriptive help text for the topic.
- example：一个或多个使用示例。（可能为空。）example: One or more usage examples. (May be empty.)
示例：HELP 'log'Example: HELP 'log'
产生：Yields:
```
Name: 'LOG'
Description:
Syntax:
LOG(X), LOG(B,X)

If called with one parameter, this function returns the natural
logarithm of X. If X is less than or equal to 0.0E0, the function
returns NULL and a warning "Invalid argument for logarithm" is
reported. Returns NULL if X or B is NULL.

The inverse of this function (when called with a single argument) is
the EXP() function.

URL: https://docs.oracle.com/cd/E17952_01/mysql-8.4-en/mathematical-functions.html

Examples:
mysql> SELECT LOG(2);
        -> 0.69314718055995
mysql> SELECT LOG(-2);
        -> NULL
```

主题列表。List of topics.

这意味着搜索字符串匹配了多个帮助主题。This means that the search string matched multiple help topics.

示例：HELP 'status'Example: HELP 'status'

产生：Yields:

Many help items for your request exist.
To make a more specific request, please type 'help <item>',
where <item> is one of the following topics:
   FLUSH
   SHOW
   SHOW BINARY LOG STATUS
   SHOW ENGINE
   SHOW FUNCTION STATUS
   SHOW PROCEDURE STATUS
   SHOW REPLICA STATUS
   SHOW STATUS
   SHOW TABLE STATUS

主题列表。List of topics.

如果搜索字符串匹配一个类别，也会显示列表。A list is also displayed if the search string matches a category.

示例：HELP 'functions'Example: HELP 'functions'

产生：Yields:

You asked for help about help category: "Functions"
For more information, type 'help <item>', where <item> is one of the following
categories:
   Aggregate Functions and Modifiers
   Bit Functions
   Cast Functions and Operators
   Comparison Operators
   Date and Time Functions
   Encryption Functions
   Enterprise Encryption Functions
   Flow Control Functions
   GROUP BY Functions and Modifiers
   GTID
   Information Functions
   Internal Functions
   Locking Functions
   Logical Operators
   Miscellaneous Functions
   Numeric Functions
   Performance Schema Functions
   Spatial Functions
   String Functions
   Window Functions
   XML

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